Adhering to a madhhab when one knows that other madhhabs have stronger evidence

If a person adheres to a particular madhhab, then he finds
out that it is likely that another madhhab has stronger evidence, this is a
serious error. It is not permissible to do that. This is included in what is
mentioned in the aayah (interpretation of the meaning): 

“They (Jews and
Christians) took their rabbis and their monks to be their lords besides
Allaah (by obeying them in things which they made lawful or unlawful
according to their own desires without being ordered by Allaah), and (they
also took as their Lord) Messiah, son of Maryam (Mary), while they (Jews and
Christians) were commanded [in the Tawraat (Torah) and the Injeel (Gospel)]
to worship none but One Ilaah (God — Allaah) Laa ilaaha illa Huwa (none has
the right to be worshipped but He). Praise and glory be to Him (far above is
He) from having the partners they associate (with Him)”

[al-Tawbah 9:31]

This implies turning away from the guidance of Allaah and the
Sunnah of His Messenger (peace and blessings of Allaah be upon him).